Rechargeable batteries such as batteries made up of many lithium-ion cells can be used in many applications, including for example in electric vehicle (“EV”) and hybrid electric vehicle (“HEV”) applications. Such batteries can generate large amounts of heat that needs to be dissipated.
A common type of lithium-ion battery cell is a hard shelled, prismatic cell having a generally rectangular prismatic shape, with six square or rectangular faces which meet at angular or rounded corners. One face of each cell typically carries the positive and negative terminals that carry the electric current. The electrochemically active components of the cell are wound and placed inside the shell, which is typically made from a metal such as aluminum or steel.
A typical prismatic lithium-ion battery cell has a length (extending along an “in-plane” direction) which is several times greater than its width (extending along a “through-plane” direction), such that the surface areas of the two opposed faces extending along the in-plane direction are significantly greater than the surface areas of the faces extending in the through-plane direction, including the face which carries the positive and negative terminals. The in-plane and through-plane faces of the prismatic battery cell are further described below with reference to FIG. 1.
In a typical construction, individual prismatic battery cells are packed together to form a battery pack, with the in-plane faces of adjacent cells either touching or in close proximity to one another, and with the outer faces of the battery pack being defined by the through-plane faces of the cells. Providing a single plate cooler in contact with the through-plane faces of the battery cells along one side of the battery pack does not, however, provide uniform cooling, and can result in significant temperature non-uniformity within the cell. While temperature uniformity can be improved by providing plate coolers along more than one face of the battery pack, the provision of multiple plate coolers requires a large number of coolant connections, which increases complexity, manufacturing cost, and the chance of leakage at a failed joint.
Also, in order to ensure adequate heat exchange, it is desired that the plate coolers are brought into intimate contact with the battery pack. However, achieving adequate compression between a single plate cooler and the face of a battery pack may be difficult, partly due to the fact that the through-plane faces of the individual battery cells and/or the plate cooler may not be perfectly flat, and/or due to misalignment of the battery cells in the pack. For example, as prismatic batteries age, bulges may form in the outer shells of the prismatic cells. This bulging can reduce contact between the battery cells and the plate coolers, thereby reducing heat transfer from the battery cells to the plate cooler.
In contrast to battery packs constructed from prismatic cells, battery packs constructed from thinner, soft-sided pouch cells, are optimally cooled by providing plate coolers to cool the in-plane faces of adjacent cells. However, in the case of relatively thick prismatic cells, cooling of the in-plane faces is less efficient than cooling of the through-plane faces. Due to its shape, the thermal conductivity of a prismatic lithium-ion battery cell is highly anisotropic, with the thermal conductivity of the through-plane faces being about two orders of magnitude higher than the thermal conductivity of the in-plane faces.
In a battery pack construction applicable to pouch cells, heat conductive fins are placed between the in-plane faces of adjacent cells, with the edges of the fins being connected to one or more fluid-carrying panels located along the sides of the battery pack. The fins transfer heat from the in-plane faces of the pouch cells to the coolant circulating through the panels. Such a battery pack is described in U.S. Pat. No. 8,383,260 to Essinger et al. Because this type of structure only cools the in-plane faces of the cells, and because it relies on indirect cooling by the heat conductive fins, it would not be expected to be effective for cooling prismatic cells.
There remains a need for providing multi-sided plate coolers for rechargeable battery packs constructed from prismatic cells, which provide improved heat transfer and temperature uniformity, without sacrificing simplicity, manufacturability and reliability.